[astro-ph/0610007] Separating the Weak Lensing and Kinetic SZ Effects from CMB Temperature Maps

Authors:  Mario A. Riquelme, David N. Spergel
Abstract:  A new generation of CMB experiments will soon make sensitive high resolution maps of the microwave sky. At angular scales less than $\sim$10 arcminutes, most CMB anisotropies are generated at z $< 1000$, rather than at the surface of last scattering. Therefore, these maps potentially contain an enormous amount of information about the evolution of structure. Whereas spectral information can distinguish the thermal Sunyaev-Zeldovich (tSZ) effect from other anisotropies, the spectral form of anisotropies generated by the gravitational lensing and the kinetic Sunyaev-Zeldovich (kSZ) effects are identical. While spectrally identical, the statistical properties of these effects are different. We introduce a new real-space statistic, $<\theta (\hat{n})^3 \theta (\hat{m})>_c$, and show that it is identically zero for weakly lensed primary anisotropies and, therefore, allows a direct measurement of the kSZ effect. Measuring this statistic can offer a new tool for studing the reionization epoch. Models with the same optical depth, but different reionization histories, can differ by more than a factor of 3 in the amplitude of the kSZ-generated non-Gaussian signal.
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Antony Lewis
Posts: 1618
Joined: September 23 2004
Affiliation: University of Sussex

[astro-ph/0610007] Separating the Weak Lensing and Kinetic S

Post by Antony Lewis » October 05 2006

This paper defines a simple component of the CMB 4-point function which they claim vanishes for lensing but provides a signature of kinetic SZ, hence allowing one to probe the latter independently.

My first comment is that they are using a series expansion in the deflection angle. As they mention this is an approximation, and in fact is not really very good (e.g. see Fig 8 of astro-ph/0601594). However doesn't the lensed < T_lens(x)^3 T_lens(y) > vanish more generally (for uncorrelated lensing potential) because T_lens is linear in T, we assume T is Gaussian and isotropic, and <T(x)^2> is unchanged by lensing?

My second comment is that the SZ signal will be correlated with the lensing signal to some extent (see e.g. astro-ph/0208325), which presumably complicates the picture.

Christopher M. Hirata
Posts: 3
Joined: January 18 2005
Affiliation: Princeton University

[astro-ph/0610007] Separating the Weak Lensing and Kinetic S

Post by Christopher M. Hirata » October 16 2006

However doesn't the lensed < Tlens(x)3 Tlens(y) > vanish more generally (for uncorrelated lensing potential)
Yes, I also get that it vanishes.

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